When it’s raining the sales clerks in the big department stores are supposed to pack your goods in a watertight way. But the weather here is prone to quick changes and a person deep inside a store would have a difficult time knowing whether the sun is currently shining or whether a wall of water is coming down from the heavens.
The Japanese have solved this in a particularly elegant way. When it’s beginning to rain, the store will play Singing in the Rain over the internal speakers and when it has stopped Over the Rainbow. That way, everyone always knows what’s up.